1. Field of the Invention
The present invention relates to a motor control method and a motor control apparatus.
2. Description of Related Art
During disassembly of for example a motor that is equipped with permanent magnets, there is known a conventional method of demagnetizing the permanent magnets by impressing a high-frequency voltage between the terminals of the windings of the motor. (For example, refer to Japanese Unexamined Patent Application, First Publication No. 2001-346364).
However, in this method, a special apparatus for impressing the high-frequency voltage on the motor is required, and there is the risk that damage may occur due to the temperature of the windings of the motor excessively rising.
To address such problems, for a hybrid vehicle that is conventionally equipped with a motor having permanent magnets and an internal combustion engine as driving sources, there is known a conventional method of performing zero torque control in which during disassembly of the motor, in the state of rotationally driving the motor with the drive power of the internal combustion engine while performing control so that the output torque of the motor becomes approximately zero, the terminal voltage of the motor is maintained at or below the power supply voltage of the battery (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2004-242398).
In the method according to the latter of the aforesaid conventional art, since zero torque control is performed so that the output torque of the motor becomes approximately zero, the charge-and-discharge current of the battery is controlled so as to become zero, and the rotational energy of the internal combustion engine is converted to thermal energy. However, according to this method, since the terminal voltage of the motor is maintained at or below the supply voltage of the battery, current is actually made to be discharged from the battery so as to compensate the losses by the motor and the inverter for motor drive control. For this reason, in the case for example of the battery being degraded, it is not possible to maintain the discharging from the battery, and so there is a possibility of difficulties arising in performing the desired demagnetization.
The present invention was made in view of the above circumstances, and has an object of providing a motor control method and a motor control apparatus that can suitably demagnetize permanent magnets provided in a motor.